The invention relates to a metal working machine, more particularly a grinder, miller or the like, having a machine head in which a rotatable tool support is disposed.
Metal working machines of the kind specified are known in which the tool support is driven by compressed air and mainly comprises an all-lubricated working spindle having a turbine wheel disposed thereon. After acting upon the turbine wheel, the oil-containing driving air is conveyed to the ball bearings disposed in the zone of the driving spindle. The air still containing a residual oil then makes its way via a gap outwards in the direction of the workpiece to be processed.
The basic advantage of oil-containing driving air/lubrication is that it enables turbines to be operated at a relatively high speed above 100 000 rpm. However, on the other hand the oil-containing driving air/lubrication has the disadvantage that it cannot be used for the processing of hard metal or under laboratory conditions, because of the excessive lubricant emissions emerging from the metal working machine via the air flow.
In addition, in the prior art the quantity of lubricant supplied is coupled with the volumetric flow of compressed air, something which results in an excess of lubricant with an increasing performance of the metal working machine.
Moreover, however, in the prior art metal working machine not only the lubricant emissions but also the noise emissions are so high that they will in future also no longer be tolerable for reasons of labour protection.
German Utility Model G 92 11 971.9 suggests that the aforementioned disadvantages should be avoided by providing the corresponding metal working machine with a compressed air duct which is intended exclusively for oil-free driving air, the bearings of the tool support being lubricated via separate ducts filled with oil mist. Moreover, in the prior art metal working machine a sound absorber is provided in the compressed air duct, by means of which the noise emitted during the operation of the metal working machine has been appreciably reduced.
Practical trials of the metal working machine known from the aforementioned Utility Model have shown that operating personnel may be endangered by the tool support continuing to run, although the compressed driving air has already been switched off. Due to this prolonged after-running, a certain time must moreover elapse after the known metal working machine has been switched off before the previously used tool can be interchanged for a fresh tool.
It is an object of the invention so to further develop a metal working machine of the kind specified as to reduce the risk of injury and shorten tool-changing times.
This problem is solved according to the invention by a metal working machine, more particularly a grinder or miller, having a machine head in which a tool support is disposed which mainly comprises a rotatable working spindle having disposed thereon a turbine wheel which can be acted upon by oil-free compressed driving air flowing via a first compressed air duct to the turbine wheel; disposed on the flow-off side in the first compressed air duct is a sound absorber via which the compressed air emerges directly to the surroundings, a second compressed air duct being provided via which the turbine wheel can be acted upon by oil-free compressed braking air which exerts on the turbine wheel an impulse directed oppositely to the operative direction of the compressed driving air; and at least one further duct is provided which extends separately from the first and second ducts and through which an oil mist flows which lubricates the driving spindle of the tool support.
The metal working machine according to the invention has in comparison with the prior art metal working machines a further compressed air duct via which compressed braking air can be conducted to the turbine wheel after the compressed driving air has been switched off. This allows the reduction to a minimum of the time during which the tool support continues to run following the switching off of the compressed driving air. Similarly, the tool can be changed practically immediately after the shutting-off of the compressed driving air. This enables compressed-air-driven metal working machines of the kind specified to be used at automated processing centres at which the individual working steps succeed one another within very short processing cycles. At the same time the risk of injury due to the after-running of the tool support is substantially precluded in the case of corresponding manually operated metal working machines. The oil mist required for lubricating the bearing of the tool support can be produced in a simple manner by the feature that disposed on the inlet side of the duct through which the oil mist flows is an atomizer which produces the oil mist.
Moreover, in a preferred embodiment of the invention the tool support has a receiving opening for the working tool. At the same time, disposed in the zone of the receiving opening for the working tool is at least one vacuum line which removes the film of lubricating oil by suction in the zone of an annular gap.
The result of the vacuum suction removal is that the emergence of oil is also appreciably reduced, so that the metal working machine can be used even in areas in which very heavy demands are made on the purity, for example, of the surrounding air. To further minimize the emergence of the lubricant, in a particularly preferred embodiment of the invention the small quantity of air transporting the oil mist can also be recollected again after flowing through the ball bearings and be freed from any residual oil by a filter element prior to its emergence into the surrounding air.
The protection of the metal working machine according to the invention against wear can be further enhanced by the feature that inside the machine head in the zone of the outlet opening at which the driving spindle extends from the machine head, a chamber is formed which adjoins a shaft seal sealing the interior of the machine head off from the surroundings and which can be filled with barrier air forming a barrier against dirt entering the machine head in the zone of the shaft seal. With such a design of the metal working machine according to the invention the compressed air dammed in the chamber counteracts both during machine operation and stoppage very fine particles of dust which otherwise might penetrate through the shaft seals into the interior of the machine head.
The versatility of the metal working machine according to the invention can be enhanced by the feature that an adapter plate can be connected to the machine head via which the machine head can be connected to any required machine frame. Such multiple utilizability is important more particularly if such a metal working machine is to be used in conjunction with existing numerically controlled metal working centres.
It is also advantageous to the assembly of the metal working machine according to the invention if the compressed air ducts terminate jointly at an outside wall of the machine head, while attachable to said outer wall is a connecting member via which the supply lines for the compressed driving air and/or the compressed braking air and/or the oil mist can be connected to the machine head.
Finally, advantageously the turbine wheel constructed in the form of a disc and its peripheral surface is formed with pockets forming the working surface for the braking air. This is a simple way of reducing the number of the constructional elements required for driving and braking the tool support.